Low-temperature reaction-sintering of mullite ceramics with an Y2O3 addition

Mullite ceramics were fabricated at relatively low temperatures from powder mixtures of α-Al2O3 and quartz, with an Y2O3 addition. The mullitization process was analyzed by X-ray diffraction. The densification behavior was investigated as a function of the Y2O3 content, sintering temperature and holding time as well as mullite seeds. It has been shown that mullitization occurs via a nucleation and growth mechanism within an yttrious aluminosilicate glass, but lattice and grain-boundary diffusion becomes important during the densification process. Moreover, the incorporation of mullite seeds was observed to enhance both mullitization and densification. At 1400°C for 5 h or 1450°C for 2 h, 15 mol% Y2O3-doped and 5 mol% mullite-seeded specimens can be sintered to almost full density.